Further, add use of it in libvpx_vp8_encoder and with tuning for keyframes and lower bound of std_dev = 1.25 to work around some edge cases. Plus some minor cleanup. Bug: webrtc:358039777 Change-Id: I6f624a6a8c7ccfe2fe656e4c089c225296f0264f Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/370061 Reviewed-by: Sergey Silkin <ssilkin@webrtc.org> Commit-Queue: Erik Språng <sprang@webrtc.org> Cr-Commit-Position: refs/heads/main@{#43513}